I have heard mad bulls fit so I would think most rails fit. I bought an Avengers 12inch. I thinks it's OEM is LaRue tactical. I got it in the mail today and will be trying to get it on in the next few days. I'll report back.

The rail, delta ring, and barrel nut all fit perfect. There is a small piece in the shape of a c. It has a notch to fit against the receiver, but it was too skinny. Also, two Alan bolts go through this piece and thread into a spacer on the other side or the barrel nut. These bolts we found to be unable to line up properly because it looks like it hits the receiver, not allowing it to seat all the way down so the bolts go in at an angle and the do not thread in. I believe this part is to further secure the rail. With out it feels solid enough. No wobble and it's really tight.